Penny Wong has indicated Labor will target the Paladin offshore detention security contract in Senate estimates this week, accusing the government of failing to explain why the company was awarded $420m in contracts through closed tender.

On Sunday the attorney general, Christian Porter defended the home affairs minister Peter Dutton, who has said he had “no sight” of the tender process. Porter told ABC’s Insiders that “standard procurement processes are often at arms-length from the minister”.